Early generations of micro electromechanical systems (MEMS) devices have shown considerable drift in their properties over time. One significant manifestation of drift is that when mirrors are actuated at full voltage (˜200V) to achieve maximum tilt (˜6°) the angle of the mirror subsequently drifts by as much as 0.5° with a long time constant, approaching days. This is unacceptable performance for MEMS devices in optical systems such as an optical cross-connect (OXC), where mirror stability is essential to maintain optical throughput. In such cases, the magnitude of drift is such that it may not even be possible to maintain an established channel, even with reasonable feedback mechanisms.
Drift in MEMS devices also affects other aspects of optical systems such as mirror “training”; the determination of the matrix elements required to route an optical input channel to an output channel. If the drift magnitude is substantial and/or the drift time constant is long, the training time becomes much longer and the training method more complicated, thus the cost of the system increases dramatically. Additionally, in operation, significant drift in an OXC compromises switching time and requires additional control mechanisms to maintain optimum optical throughput during the settling time.
One current solution to reducing the deleterious effects of drift in MEMS devices includes the implementation of shielding of the insulating region from the movable MEMS element. This method though, is not completely effective or reliable and adds cost to the MEMS devices.